Mixed-flow pump with variable flow area

ABSTRACT

The effective blade height of a pump employing a fixed lead conical impeller is adjusted to vary the pump flow area in accordance with load. Blade height adjustment is achieved by imparting axial and rotational movement to a &#39;&#39;&#39;&#39;threaded&#39;&#39;&#39;&#39; impeller hub with respect to the impeller blades and front shroud.

United States Patent 1191 Grennan Apr. 23-, 1974 [5 MIXED-FLOW PUMP WITH VARIABLE 2,683,419 7/1954 Schneider. .1 415/131 FLOW AREA 2,927,536 3/1960 'Rhoades 1 415/141 X 3,116,696 l/1964 Deters 415/141 UX Inventor: Charles Grennan, g o 3,265,001 8/1966 Deters ..415/141-ux Conn.

73 Ch dl E I w t FOREIGN PATENTS OR APPLICATIONS 1 .sslgnee' 3 3- es 1,045,593 12/1958 Germany 416/186 A [22] Filed: 7 Primary Exa minerEverette A. Powell, Jr. [21] Appl. No.1 277,593 1 1 57 ABSTRACT 52 US. Cl 416 149 416133, 416177 1 i511 1111. c1. .1 F04d 2 9/28 The w' blade 116181 Pump employmg a 58 Field ofSear ch 416/133 149 150 176 fixed lead/COM! impeller is adjusted to vary the 416/l77. 6 pump flow area in accordance with load. Blade height adjustment is achieved by imparting axial and rota- [56] References Cited tional movement ma threaded impeller hub with UNITED STATES PATENTS respect to the impeller blades and front shroud, 2,133,853 10/1938 Feige 416/133 17 i 7 Claims 2 Drawing Figures 1 MIXED-FLOW PUMP WITH VARIABLE FLOW AREA BACKGROUND OF THE INVENTION The present invention has been found to be particu-' larly well suited for use with centrifugal pumps having a conical or mixed-flow impeller; such pumps having an axial inlet and radial discharge for fluid delivered thereto. As is well known, while centrifugal pumps are variable displacement machines, variation in flow at fixed-speeds eauses an attendant reduction in overall pump efficiency when such pumps are operated at off- 7 design flow conditions. The reduction is pump efficiency due to partial loading becomes acute at extremely low flow s; the lost horsepower due to inefficiency significantly overheating the process fluid under low flow conditions. In many cases overheating of the process fluid will cause damage to equipment and/or deterioration of the fluid itself. Nevertheless, there are many applications for mixed-flow centrifugal pumps wherein a high turn-down ratio is required. Thus, by way of example, boost pumps for gas turbine engines are required to operateat fixed speed with both full and partial loading; i.e., with high and low flow.

As briefly noted above, prior art attempts to operate mixed flow centrifugal pumps, and particularly those pumps having impellers designed for high flow rates, under partial load conditions have resulted in a reduction in efficiency and overheating. The poor efficiency of prior art pumps when operating under less than design flow conditions resulted from the fact that at low flow rates the impellers exhibited viscous and counterflow losses. To avoid the problem of poor efficiency at low flow rates, while permitting the realization of the inherent advantages of mixed flow type centrifugal pumps, industry has resorted to the use of pairs of pumps in parallel. For example, the aerospace industry has used pumps paralleled on the same drive shaft with a clutch mechanism for permitting the selective operation of one or both pumps in the interest of solving the turn-down problem. As will be obvious to those skilled in the art, the use of two pumps resulted in a larger, heavier and more costly pump package.

For the reasons briefly stated above, there has long been a desire in the art to provide a mixed-flowcentrifugal pump having a high turn-down" ratio. If such a pump could be produced there would obviouslybe imed-flow centrifugal pumps have conventionally sought to vary the geometry of a stationary part of the pump. Thus, by way of example, it has been prpposed in the prior art to vary the area of the inlet port or of a feedback passage extending between the discharge and inlet ports of conical impeller pumps. These prior art efforts to improve the partial loacl efficiency of mixedflow centrifugal pumps have not met with commercial success due to inherent design deficiencies. For examples of prior art approaches to solving the turn-down" problem, reference may be had to US. Pat. No. 3,168,870 and 3,442,220; the latter patent disclosing a pump of the same type as that with which the present invention is concerned.

SUMMARY OF THE INVENTION The present invention overcomes the above discussed and other problems of the prior art by providing a novel and improved mixed-flow centrifugal pump which is characterized by a variable flow area. In accordance with the invention the effective blade height of a fixed lead conical impeller may be adjusted to meet the required flow conditions. The blade height adjustment in accordance with the present invention is achieved through varying the positioning of a threaded impeller hub with respect to the impeller blades and pump front shroud. The threads in the impeller hub match the lead of the blades and the hub may therefor be caused to engage more or less blade height to adjust the flow area. In accordance with the inven-. tion, the fluidic impelling surfaces; i.e., the impeller blades; are not driven through the hub as in prior art practice. Rather, a shaft protrudes through the hub and attaches to the blades at the front of the impeller. The tip shroud, which is attached to the impeller blade tips, retains the blade tips in position throughout the impel: ler length.

Automatic adjustment in accordance with the present invention may be accomplished by directly employing the change in momentum of the varying flow, by sensing and employing the change in pressure rise by the varying flow or by use of a servo actuatorwhich reacts directly to the flow rate. In accordance with a preferred embodiment, a coil spring is employed to move. the hub both axially and radially in accordance with the dynamic and fluid dynamic loading on the hub.

i BR EF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the two figures and in which:

FIG. 1 is an exploded side elevation view, partly in section, of the impeller-hub assembly of a pump cordance with the present invention; and

FIG. 2 is a cross-sectional, top view of a variable mixed-flow centrifugal pump in accordance with a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now simultaneously to FIGS. 1 and 2, a pump in accordance with the present invention includes a fixed lead conical impeller 10. The root of the impeller blade is integral with or suitably affixed to a pump drive shaft 12. Drive shaft 112 extends through a unique hub assembly 14 and is coupled to a suitable prime mover. The tips of the conical impeller blade are attached, for example by welding, to a tip shroud mem in acber 16 whereby shroud member 16 holds the blade tips in position throughout the impeller length. Since shroud member 16 rotates with the impeller a suitable wear ring or stationary seal, indicated schematically at 18 in FIG. 2, is provided between shroud l6 and the pump housing 20. Housing 20 defines the axial inlet port 22 and radial discharge port 23 for the pump.

The hub assembly 14 includes a generally conically shaped forward section 24 which is complementary in shape to the dimensions of the passage defined by impeller 10. As will be explained in greater detail below, hub member 14 rotates with and is both axially and radially movable with respect to impeller 10. The conical forward section 24 of hub 14 is provided with a thread 26 which matches the lead of the impeller blade. At this point it is worthy to note that FIG. 2 depicts the pump of the present invention operating under full load conditions at its design speed. FIG. 1 depicts the impeller and hub assemblies separated to an inoperated position in the interest of clarifying the structure of the invention. In operation the thread or slot in the hub is always engaged, at least to the extent shown in FIG. 2, with the impeller blade whereby the blade drives the hub.

The present invention operates by adjusting the effective impeller blade height for the particular flow conditions. This adjustment of blade height is achieved through the variable positioning of hub 14 with respect to the blade of impeller 10 and the impeller front shroud 16. As previously noted, the threads 26 in impeller 14 match the lead of the impeller blade and the hub may thus be caused to engage more or less blade height to adjust the flow area. This adjustment action is achieved driving the hub toward inlet port 22 while simultaneously turning the rotating hub with respect to the rotating blade so as to screw" the hub onto the impeller blade.

The above described adjustment procedure may be accomplished in several ways. However, in accordance with the disclosed preferred embodiment, adjustment of the effective blade height is achieved automatically through the use of a coil spring 28 which extends between an inner shoulder on hub 24 and a collar 32 which is attached to and rotates with shaft 12. Spring 28 is used in a torsional condition and is preloaded in the forward direction; the spring opposing the dynamic load which tries to move the hub away from the impeller blade. With design flow conditions spring 28 will be compressed as shown. Should the load decrease, signifying the need to vary the pump geometry by reducing the effective blade height, there will be a reduction in momentum forces acting on hub 24. The reduction in momentum forces will permit spring 28 to overcome the dynamic and hydraulic loads on the hub and to urge the hub forwardly toward the impeller while simultaneously partially rotating the hub with respect to the impeller. The minimum flow position is indicated in FIG. 2 by a broken line. The hub will thus assume a new position commensurate with the instantaneous flow conditions and, at this new hub position, the pump will be carrying less flow than an equally design rated prior art pump with a conventional stationary hub. Accordingly, the pump of the present invention will operate with higher'efficiency at off-design conditions when compared to the prior art.

While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it will be understood that the present invention has been described by way of illustration and not limitation.

What is claimed is:

1. In a rotary-pump including an impeller having at least one cambered blade of screw-like configuration affixed to a drive shaft, means for varying the pump capacity comprising:

a hub member rotatable with the pump impeller, said hub member having a slot formed therein, said hub member slot matching the lead of the impeller blade and at least partly engaging the blade; and

means for moving said impeller hub member axially with respect to the impeller while simultaneously rotating said hub member with respect to the rotating impeller blade whereby the degree of engagement between said slot and the impeller blade may be varied to adjust the effective blade height.

2. The apparatus of claim 1 wherein the impeller further comprises:

. a frustoconical shroud member attached to the impeller blade for holding the blade tips in position throughout the impeller length.

3. The apparatus of claim 2 wherein the impeller drive shaft extends through said hub member and wherein engagement between said hub member slot and impeller blade cause said hub member to rotate with the hub.

4. The apparatus of claim 1 wherein the impeller drive shaft extends through said hub member and wherein engagement between said hub member slot and impeller blade cause said hub member to rotate with the hub.

5. The apparatus of claim 1 wherein said means for causing movement of said hub comprises:

means responsive to the dynamic forces applied to I said hub member for automatically positioning said hub member with respectto the impeller in accordance with the pump load. t 6. The apparatus of claim 3 wherein said means for causing movement of said hub comprises:

means responsive to the dynamic forces applied to said hub member for automatically positioning said hub member with respect to the impeller in accordance with the pump load. 7. The apparatus of claim 6 wherein said means for automatically positioning said hub member comprises:

flow. 

1. In a rotary pump including an impeller having at least one cambered blade of screw-like configuration affixed to a drive shaft, means for varying the pump capacity comprising: a hub member rotatable with the pump impeller, said hub member having a slot formed therein, said hub member slot matching the lead of the impeller blade and at least partly engaging the blade; and means for moving said impeller hub member axially with respect to the impeller while simultaneously rotating said hub member with respect to the rotating impeller blade whereby the degree of engagement between said slot and the impeller blade may be varied to adjust the effective blade height.
 2. The apparatus of claim 1 wherein the impeller further comprises: a frustoconical shroud member attached to tHe impeller blade for holding the blade tips in position throughout the impeller length.
 3. The apparatus of claim 2 wherein the impeller drive shaft extends through said hub member and wherein engagement between said hub member slot and impeller blade cause said hub member to rotate with the hub.
 4. The apparatus of claim 1 wherein the impeller drive shaft extends through said hub member and wherein engagement between said hub member slot and impeller blade cause said hub member to rotate with the hub.
 5. The apparatus of claim 1 wherein said means for causing movement of said hub comprises: means responsive to the dynamic forces applied to said hub member for automatically positioning said hub member with respect to the impeller in accordance with the pump load.
 6. The apparatus of claim 3 wherein said means for causing movement of said hub comprises: means responsive to the dynamic forces applied to said hub member for automatically positioning said hub member with respect to the impeller in accordance with the pump load.
 7. The apparatus of claim 6 wherein said means for automatically positioning said hub member comprises: resilient means for applying torsional force to said hub member, said resilient means being preloaded in the full flow condition to urge said hub member axially and radially to a position commensurate with reduced blade height upon a reduction in flow. 